1. Field of the Invention
The present invention relates to a printing apparatus and to a control method and a program for the printing apparatus, and particularly relates to a printing apparatus that outputs an additional image, such as a copy-forgery-inhibited pattern image, and a control method and a program for the printing apparatus.
2. Description of the Related Art
In the printing industry today, four (or full) color, CMYK printing is most commonly employed for color printing. However, since such color printing requires materials, e.g. toners or inks, for printing four different colors (which are combined in varying proportions to create the full range of colors), the operating costs are high. As one result of this, M color printing has become the object of attention where denotes a value of two or greater, and equal to or smaller than, a value of N−1, where N denotes the number of color materials available or loading into a printing apparatus (so N denotes the number of different color materials that can be loaded into a printing apparatus). Thus for a four-color printing apparatus (where N is 4), M is 2 or 3.
A two-color printing technique is disclosed in Japanese Patent Laid-Open No. 2005-022283. According to this conventional art, the printing of images is performed using only two, user-selected colors.
Furthermore, an additional image, such as a copy-forgery-inhibited pattern image, is disclosed in this conventional art, and for this image, the user is also permitted to select the color to be employed. Specifically, the user may not only selectively designate the two colors for normal printing, but may also select the color to be used for the additional image. Thus, since the user can select the individual and arbitrary colors both for normal printing and for the additional image, there is a case wherein the colors used for normal printing and for the additional image differ, i.e., wherein a color not to be used for normal printing is designated as the color for the additional image.
That is, when a color selected to be used for an additional image is included as either of the colors selected for normal printing, no problem will be encountered in performing printing in accordance with the user's selections. However, a problem does occur when a color selected for an additional image is not included among the colors chosen for normal printing. In this case, although the number of colors used for normal printing is reduced to two, another color must be prepared and used for printing the additional image, and the desired effects provided by limiting the number of colors can not be obtained. In Japanese Patent Laid-Open No. 2005-022283 above, this problem is resolved by changing the color selected for the additional image, i.e., by changing the color selected for the additional image to one of the two colors, other than black, selected for normal printing. It should be noted here that a copy-forgery-inhibited pattern image (e.g. a security pattern image such as a copy-deterrent pattern image) is formed using large dots and small dots, and in printed matter, it is difficult for persons to see a difference in the densities between an area wherein large dots were deposited and an area wherein small dots were deposited, but on a duplicate obtained by copying this printed matter, it is easy to see the difference in the densities on the duplicate. The difference in the densities thus indicates to a reader that the duplicate is unauthorized. This occurs because the small dots may have disappeared or have become faded while being copied. When an additional image is employed only for documents for which reproduction is restricted, unauthorized use can be prevented.
When the color for an additional image is changed to a color other than black, a relatively more expensive color material (a toner or an ink) is employed for printing the additional image. This is an especially great problem for Japanese Patent Laid-Open No. 2005-022283, because the color originally selected by a user for an additional image is changed and a different substitute color is employed, and as a result of the employment of this color for the additional image, a higher color cost is incurred. When cyan, for example, is employed as the color for an additional image, the color cost is increased because cyan material is generally more expensive than black material. Moreover, when blue, for example, is selected as the color for an additional image, two color materials, cyan and magenta, are actually employed, and the color cost becomes even greater.
The present invention is provided to resolve the color cost problem. According to this invention, when a color selected for an additional image is not included among a plurality of colors selected for use for normal printing, the color selected for an additional image is changed to a proper color. One advantage of the present invention is to provide a printing apparatus that suppresses increase in cost by changing a color to be used for an additional image in the above described manner, and a control method and a program for the printing apparatus.